1. Field of the Invention
The present invention relates to an electrically conductive rod-shaped single crystal product which is useful for e.g. a probe pin for measuring electrical properties of a semiconductor integrated circuit, a fine vacuum device or an electron gun, or a probe for a scanning type probe microscope such as a scanning tunnel microscope or an inter-atomic force microscope, and an assembly for measuring electrical properties employing such a single crystal product.
2. Discussion of Background
Heretofore, various materials having electrical conductivity or electron radiation have been used for a probe pin for measuring electrical properties of a semiconductor integrated circuit, a fine vacuum device or a electron gun, or a probe for a scanning type probe microscope such as a scanning tunnel microscope or an inter-atomic force microscope. For example, the probe pin for measuring electrical properties of a semiconductor integrated circuit, is used for a probe card for measuring electrical properties to remove defective products in the process for producing a semiconductor integrated circuit. Hereinafter, a specific description will be made with respect to the probe pin for measuring electrical properties of a semiconductor integrated circuit. In the production of LSI, measurement is carried out to test the operation of a circuit element constituting each chip, at a stage when a circuit element is produced in a wafer. Thereafter, when a chip cut off from the wafer, has been packaged or mounted on a TAB tape, measurement is carried out again for testing the operation. For the former test, it is common to employ a probe card having a probe pin made of a metal such as tungsten. The latter test is carried out by using a socket, to which an outer lead is inserted, in many cases. However, in the case of TAB, a probe card may sometimes be used. In such a probe card, a probe pin made of tungsten is used in most cases, and its forward end is bent so that it will be resiliently in contact with an electrode of a semiconductor to be evaluated. In a probe card, it is common that a plurality of probe pins will be brought into contact with electrodes of a semiconductor to be evaluated. Accordingly, it is necessary to absorb errors in e.g. the flatness of the forward ends of the probe pins, the flatness of the electrodes of the semiconductor to be evaluated and their parallelism when they are set in an evaluation apparatus. For this purposes in the case of tungsten wires, probe pins are designed to bend. The degree of bending of the probe pins is referred to as overdrive. A probe card using a tungsten wire is designed so that this overdrive can be exerted up to 100 .mu.m. Current probe cards are prepared so that such probe pins are positioned and fixed individually so that they agree to the positions of the electrodes of a semiconductor to be evaluated. However, with a rapid progress in refinement of semiconductors, it has become difficult to fix probe pins accurately and highly densely, and preparation of probe cards has reached the limit.
Under the circumstances, a probe card has been devised wherein fine probe pins are planted on a substrate vertically or with a proper angle of inclination. For example, methods have been proposed in which single crystals are formed on a silicon substrate with their positions controlled by a vapor-liquid-solid methods and they are used as probe pins for a probe card (Japanese Unexamined Patent Publications No. 198636/1993, No. 215774/1993 and No. 218156/1993). In these methods, single crystal pins are grown on a silicon substrate with their positions controlled, and they are further processed e.g. by plating to have electrical conductivity, and such a substrate using the electrically conductive rod-shaped single crystal products as probe pins, has been used for a probe card (hereinafter the electrically conductive rod-shaped single crystal product of the present invention includes a probe pin for a probe card, and an assembly for measuring electrical properties using such a probe pin includes a probe card, but they may be called a probe pin and a probe card, respectively).
However, conventional probe pins prepared by a vapor-liquid-solid method had the following problems.
1 The ratio of the forward end diameter of a probe pin to the length of the pin is called an aspect ratio. If this aspect ratio is small, overdrive can not be applied to probe pins, and in measurement by means of a plurality of probe pins, it is difficult to let all of the probe pins contact the electrodes of a semiconductor for evaluation. Further, flexible deformation within a resilient range of probe pins by overdrive can not be expected, and probe pins are likely to break. When the aspect ratio is too large, operation efficiency tends to be poor in the preparation and use, and probe pins tend to break. Further, probe pins tend to buckle and contact each other, and the load when contacted tends to be so small that a constant electrical conductivity can not be obtained.
2 If the diameter of probe pins is too small, the probe pins are likely to break. On the other hand, if it is too large, they can not meet the requirement for high density of semiconductor terminals.
3 If the material of the conductive film is not proper, the conductive films at the forward ends of probe pins tend to peel off by repeated contact of some ten thousand times, and the life of the probe pins tends to be short.
4 If the film thickness of the conductive plating is too thin, the electrical resistance of the probe pins tends to be high. On the other hand, if it is too thick, the resiliency of the probe pins tends to be impaired, whereby the probe pins are likely to deform
5 Further, the single crystal grown on a substrate by a vapor-liquid-solid method is made to be electrically conductive and can be used by itself as a probe pin for a probe card. However, when larger overdrive is required, the probe pin is likely to break at its base portion, and it will be necessary to reinforce the base portion.
6 When probe pins are to be bonded on a circuit board, such bonding is difficult, and an easier simpler method is desired.
7 If the inclination of a probe pin to a semiconductor terminal is not proper, when contacted, the probe pin slips on the terminal and may be dislocated.
8 When many probe pins are formed with a narrow pitch from one another, it is difficult to lead-out wires from the probe pins, because with a currently available technique of photolithography employing an insulating substrate using glass, epoxy or the like, it is very difficult to conduct processing including wiring of an insulating substrate with such a fine pitch as is equivalent to LSI produced by a semiconductor technique, and even if such a processing is possible it will be highly costly.